Identification plates

ABSTRACT

A method of manufacture of an identification plate: comprises advancing a transparent sheet material having an opaque material in contact with one major surface thereof to a printing station, printing indicia in reverse on the other major surface of the sheet material, and securing the printed sheet material to a substrate having a retro-reflective surface such that the printed surface is in contact with, or at least adjacent to, the retro-reflective surface.

[0001] This invention relates to Identification plates and, Inparticular, to plates which indicate the provenance of an object towhich they are attached. Such plates are conventionally termed licenceor number plates when attached to a motor vehicle.

[0002] From Sep. 1, 2001, each United Kingdom licence plate must conformto British Standard BSAU 145 d which governs, inter alia, the impactresistance and the minimum retro-reflectivity of the plate. Similaralthough, in some cases, less stringent provisions exist across theentire European Union, as they do in most other countries across theworld.

[0003] GB 2126386 A discloses a method of producing licence plates for avehicle, in which indicia are printed onto a carrier. The carrier may beeither a reflective surface or a plastics coating, such as a relativelythick transparent plastics sheet to provide structural support for theplate.

[0004] EP 0806752 A1 discloses an identification plate and a method ofmanufacture of such a plate wherein a rigid transparent substrate hasindicia printed thereon. The resulting printed plate is then adhered toan opaque liner such that the indicia are visible through thetransparent sheet.

[0005] It is known to print on to a nominally retro-reflective surfaceand then to adhere to that surface a lens, such as a clear polymerlayer, to impart to that surface a retro-reflective character. The lensmay be a transparent, relatively thick, acrylic layer applied over theretro-reflective surface or a relatively thin layer with a relativelythick backing layer to provide support, as is disclosed in WO 94/19769A2.

[0006] Retro-reflective sheet material is typically a beaded substancewhich has a rough surface. Consequently, it is difficult to print on, sospecial formulations of sheet materials, which are able to ‘take’ theink, special printing materials such as ribbons, together with the useof elevated print-head temperatures are required. Both of these factorsincrease the cost. The coarse surface structure of the speciallyformulated retro-reflective sheet materials can reduce print-headoperating life and the elevated print-head temperatures can also reduceprint-head lifetimes. It has also been found that print quality suffersat elevated print-head temperatures and with such rough surfaces.

[0007] It is an object of this invention to provide identificationplates which can be manufactured by either a continuous process or as anindividual plate. It is a more specific object to provide methods ofmanufacture which are simpler than prior art methods, enabling moreefficient assembly of the necessary components and which have reducedthe costs compared with known methods. It is a further object of theinvention to provide methods of manufacture which provide a manufacturerwith a greater degree of flexibility in production, allowing bespoke or“multi-run” plates to be produced.

[0008] According to a first aspect of the invention there is provided amethod of manufacture of an identification plate, the method comprising:

[0009] advancing a transparent sheet material having an opaque materialin contact with a first major surface thereof to a printing station;

[0010] printing indicia in reverse on to a second major surface of thesheet material;

[0011] securing the printed sheet material to a substrate having aretro-reflective surface such that the printed surface is in contactwith, or at least adjacent to, the retro-reflective surface.

[0012] A more specific aspect of the invention provides a method ofmanufacturing an identification plate, the method comprising:

[0013] advancing a substrate-sized length of transparent sheet materialto a printing station, the sheet material having an opaque substance incontact with one major surface thereof;

[0014] optically sensing passage of the leading edge of thesubstrate-sized length of transparent sheet material by attenuation ofan optical beam by the opaque substance;

[0015] printing indicia in reverse on the other major surface of thesheet material;

[0016] securing the printed transparent sheet material to a substratehaving a retro-reflective surface such that the printed surface is incontact with, or at least adjacent to, the retro-reflective surface; and

[0017] removing the opaque material from the transparent sheet material.

[0018] A further aspect of the invention provides an identificationplate comprising a supporting substrate having two opposed majorsurfaces, the entire first major surface being retro-reflective, atransparent sheet material having indicia printed thereon, thetransparent sheet material being adhered to the first major surface suchthat the indicia are located adjacent the first major surface.

[0019] There is further provided, by a fourth aspect of the invention,an identification plate comprising a supporting substrate having aretro-reflective major surface and an transparent sheet material anentire major surface of which having marking material applied thereto,the transparent sheet material being adhered to the retro-reflectivemajor surface such that the marking material is in contact with, or atleast adjacent to, the retro-reflective major surface.

[0020] A fifth aspect of the invention provides a method of manufactureof an identification plate, the method comprising:

[0021] conveying a transparent sheet material toward printing means;

[0022] optically sensing the passage of the transparent sheet materialas it is conveyed toward said printing means;

[0023] actuating printing means in response to said passage of thetransparent sheet to print indicia in reverse on the other major surfaceof the sheet material; and

[0024] securing the printed sheet material to a substrate having aretro-reflective surface such that the printed surface is in contactwith, or at least adjacent to, the retro-reflective surface.

[0025] In a fourth aspect of the invention, there is provided anidentification plate comprising a laminate of a support and atransparent sheet material having indicia printed on a surface thereof,the support comprising a matrix material in which is retained aplurality of reflective particles, wherein the indicia are in contactwith or are at least adjacent to a major surface of the support and thetransparent sheet material provides a lens for the reflective particleslocated at that major surface, thereby providing the plate with aretro-reflective character.

[0026] A further aspect of the invention provides a method ofmanufacture for an identification plate, the method comprising the stepsof:

[0027] providing a support having reflective particles distributed in amatrix, wherein the particles are at least present at a first surface ofthe support;

[0028] printing indicia, in reverse, on a surface of a transparent sheetmaterial;

[0029] adhering the sheet material to the first surface of the supportso that the indicia are sandwiched therebetween;

[0030] whereby the sheet material acts as a lens for the particles,imparting a retro-reflective character to the plate.

[0031] The reflective particles may be uniformly distributed throughoutthe support or may be uniformly and/or preferentially distributed at ortowards the surface thereof.

[0032] The support may be formed by moulding a substance havingreflective particles therein. The support may be formed by laminating aretro-reflective sheet material to a substrate. The support may have anextension portion, for example an elongate lip. The support may compriseone or more frangible portions.

[0033] Techniques are known for preferentially distributing particles ata surface of a moulded article. Such techniques include gravityseparation whilst the matrix material is in a fluid state, which mayrely on a difference in density between fluid matrix material and theparticles, or preferential drying of one or another surface of the mouldby microwave energy or other means.

[0034] The reflective particles may be formed of glass, for exampleglass beads or spheres, or they may be formed from a mineral or aplastics material.

[0035] The support may be formed from a plastics material, for exampleacrylonitrile butadiene styrene (ABS), polyethylene, Nylon (RTM) orother hard-wearing, impact and/or bend resistance plastics materials. Insome embodiments the substrate may be formed from a metal or an alloy,for example aluminium or steel.

[0036] Preferably, the transparent sheet material is a polymer which,advantageously, may be polyvinyl chloride, polyester, polypropylene orthe like.

[0037] Preferably, the plate has a main body for primary indicia. Anextended portion for further indicia may be provided. The extendedportion may be along one of the longer sides of the plate.

[0038] Suitable retro-reflective sheet materials are either coated ornon-coated. In such coated sheet materials, a thin acrylic layer isapplied to the beaded surface, thereby providing those reflectiveparticles with a lens and imbuing the sheet material withretro-reflective characteristics. In non-coated retro-reflective sheetmaterials the surface is only provided with a retro-reflective characteronce a lens has been applied to it. With such non-coatedretro-reflective sheet materials, when used in the methods disclosedabove, the lens is provided by the transparent material and it is onlyonce this material has been applied to the retro-reflective materialthat the whole ‘sandwich’ acts retro-reflectively. Whilst non-coatedretro-reflective materials are typically less expensive than the coatedones and for that reason may be preferred, it is possible to use eitherin the methods disclosed herein.

[0039] The transparent sheet material may be supplied on a roll, or asindividual substrate-sized lengths. If the transparent sheet material issupplied on a roll, it may be shaped as a repeating pattern, each repeatthereof corresponding to a substrate-sized length.

[0040] The opaque material may be a release sheet, in one embodiment apaper release sheet. Alternatively, the opaque material may be aplastics release sheet, such as a polypropylene sheet. The release sheetmay be provided with a pressure sensitive emulsion adhesive layer, thetransparent material may have a silicone layer applied thereto, thesilicone layer which is contacted by the adhesive layer of the releasesheet facilitates separation of the release sheet and sheet material.The silicone layer and adhesive layer allow the release sheet and sheetmaterial two to be releasably adhered, such that the release sheet maybe re-applied to the transparent material.

[0041] Said printing means may be arranged to print over some, most, orall of the transparent sheet material.

[0042] The transparent sheet material may have secondary and/or otherinformation printed on the other major surface prior to being advancedto the printing station. The printing, on the transparent sheetmaterial, of any secondary and/or other information may be completed‘off-line’, which is to say that information may be printed and thetransparent sheet material stored or held for future use. The printingof secondary and/or other indicia may be completed immediately before orafter printing of the primary indicia.

[0043] Said printing means may preferably comprise a thermal masstransfer printer or an ink jet printer.

[0044] A further aspect of the invention provides a medium to bearindicia for use in an identification plate, the medium comprising atransparent plastics film carrying a silicone material on a first majorface thereof and an opaque liner carrying a pressure sensitive adhesiveon a major face thereof; a second major face of the transparent plasticsfilm being printable to, wherein the silicone layer and adhesive layerare in contact and the opaque liner and transparent film are separableand re-attachable by virtue of the releasable interaction betweensilicone layer and adhesive layer.

[0045] In order that the invention may be more fully understood, it willnow be described, by way of example only, and with reference to theaccompanying drawings, in which:

[0046]FIG. 1 shows a schematic representation of a method according tothe invention;

[0047]FIG. 2 shows a schematic representation of a variant methodaccording to the invention;

[0048]FIG. 3 shows a section through a printable medium according to theinvention;

[0049]FIG. 4 shows a detail of part of the method described inaccordance with FIG. 2;

[0050]FIG. 5 shows a section through an identification plate made inaccordance with the invention;

[0051]FIG. 6 shows section through a further identification plate madein accordance with the invention;

[0052]FIG. 7 shows an elevation of an identification plate made inaccordance with the invention;

[0053]FIG. 8 shows an elevation of a further identification plate madein accordance with the invention;

[0054]FIG. 9 shows a detail of a printer;

[0055]FIG. 10 shows an elevation of a yet further identification platemade in accordance with the invention;

[0056]FIG. 11 shows a section through the plate of FIG. 8;

[0057]FIG. 12 shows an elevation of the plate of FIG. 8 from the reverseside;

[0058]FIG. 13 shows an elevation of the plate of FIG. 8 subsequent touse; and

[0059]FIG. 14 shows a variation of the apparatus of FIG. 2.

[0060] Referring firstly to FIG. 1, a length of medium 1 to be printedupon comprising a length of transparent film 2, having an opaque releaseliner 3 in contact with one major surface thereof, is advanced in thedirection of arrow A. Among other advantages, which will becomeapparent, the release liner 3 provides the length of film 2 with somerigidity, making it easier to handle. The transparent film 2 ispreferably polyester film with a thickness of about 70 μm. The opaquerelease liner 3 is preferably paper or polypropylene with a thickness ofabout 80 μm.

[0061]FIG. 3 shows a cross-section of the medium 1. The release liner 3has a pressure sensitive adhesive emulsion layer 3 a applied thereto,that layer is typically 10 to 15 μm thick. The transparent polyesterfilm 2 has a layer of silicone 2 a applied thereto, which is typicallyabout 3 to 5 μm thick. The silicone layer 2 a is in contact with theadhesive layer 3 a. The silicone layer 2 a prevents complete adhesionbetween the adhesive layer 3 a and transparent film 2, and allows therelease liner 3 to be removed and reapplied to the transparent film 2.This allows inspection of the completed plate and re-application of therelease liner 3 to protect the surface during transit to a point of useor storage.

[0062] The printable medium 1 is brought to a printer 5 which is athermal transfer printer having a printing head 6 and a ribbon 7.Mounted either externally or internally of the printer 5 is an opticalsensing device 8, comprising an optical beam generator 9 and a detector10, located on opposite sides of the path of travel of the medium 1.

[0063] The output of the optical beam generator 9 is detected by thedetector 10 in the usual way so that any non-optically transparentmedium which interrupts the beam causes a reduction in the signaldetected by the detector 10. The signal detected by the detector 10 canbe used to control operation of the printing head 6. For example, if thedetected signal rapidly decreases, due to attenuation of the beam, thereduction is detected by signal processing means 11, such as a computer,which, in turn, controls the printing head 6 to print on the film 2.Clearly, the speed at which the medium 1 is conveyed should be monitoredand/or controlled. Monitoring the time between maximum signals and thespeed at which the medium 1 is conveyed allows accurate control of thelocation of so-printed indicia.

[0064] As the printable medium 1 passes through the optical beam, thesignal detected by the detector 10 reduces, due to the presence of theopaque release liner 3. The signal processing means 11 responds to thereduction of detected signal to control the printing head 6 to start andfinish printing the desired indicia on the transparent film 2, inreverse. That is to say that the printer 5 prints on the underside, asshown in FIG. 1, of the transparent film 2. The opaque liner 3, whichhas a rougher surface than the transparent sheet material 2 and addsextra effective thickness, enables the rollers of the printer to bothgrip the medium 1 and keep it in accurate registration and thereby printonto the transparent film 2.

[0065] A computer, which may or may not be the same as said signalprocessing means 11, holds a store of the indicia desired to be printedonto the medium 1. The information is transmitted to the printer 5 whichpreferably arranges the formatting of the desired indicia. An eminentlysuitable and preferred printer is a QLS4100 series, supplied byAstro-med Incorporated of Rhode Island, USA. The print rate of such aprinter can be as high as 20.4 cm per second, but is more typicallyoperated at 7.6 cm per second. Therefore, using such a printer withoptical control, up to 1200 standard British vehicle licence plates(52.1×11.1 cm) per hour can be produced automatically.

[0066] The resulting printed medium 15 is advanced to a laminationstation 17. A length of substrate 20 moulded from ABS with aretro-reflective surface 22 is also advanced to the lamination station17. The substrate 20 is typically from 2.5 to 3.8 mm thick, preferably3.2 mm thick. The substrate has a release sheet 23 covering apressure-sensitive adhesive layer (not shown). The adhesive layer hasbeen previously applied, i.e. off-line, although it may be applied aspart of the process. The release sheet 23 is removed as the substrate 20is advanced to the lamination station 17.

[0067] The printed medium 15, comprising transparent film 2 and opaquerelease liner 3, and the length of substrate 20 are shown as beingrectangular, with right-angle corners. Other shaped corners arepossible, for example, each of the components 2, 3, 20 may have curvedor radiused corners.

[0068] The so-formed laminated composite 30 is advanced to a furtherpoint where the opaque releasable liner 3 is removed from thetransparent film 2, thereby providing a finished identification plate40. Removal of the release liner 3 may be carried out prior to orsubsequent to installation of the plate 30 on a vehicle so that thesurface of the plate 30 is protected during transit. The silicone layer2 a will be removed by the action of the elements, precipitation, windand so on.

[0069] The transparent film 2 acts as a lens for a non-coatedretro-reflective surface 22 providing it with a retro-reflectivecharacteristic. As the lens for the retro-reflective surface 22 issimply a thin film 2 rather than a thick, transparent substrate, as isthe case in certain prior art techniques, it is found that the indiciaare clearer and the plate 40 has a higher retro-reflectivity (due to themuch shorter path length for impinging and reflected light), both ofwhich are desiderata of vehicle licence plates. When coatedretro-reflective surfaces 22 are utilised, the thin film 2 does notimpair the retro-reflective character of the surface 22.

[0070] The above description has concentrated on what may be calledindividual or ‘single-shot’ printing. However, what may be termedcontinuous, ‘batch’ or web printing may also be used, wherein a lengthof printable medium 1′ comprising a web of transparent film 2 providedwith a releasable backing layer 3 is delineated into substrate-sizedlengths by transverse perforations 4, as shown in FIG. 4. The individuallengths are shaped with rounded corners 18.

[0071] Referring to FIGS. 2 and 4, the printable medium 1′ (in FIG. 2)is shown as an individual length for the sake of clarity but, as will beappreciated, the medium 1′ is a continuous length or web. The medium 1′is advanced to the printer 5, as indicated by arrow A. As a lengthpasses over the optical beam generator 9, the detected signal reaches amaximum when a ‘viewing window’ 12, formed by the rounded corners 18 ofadjacent individual lengths of printable medium 1′, is directly in thepath of the optical beam. The maximum detected signal will correspond towhen the least amount of beam-attenuating material lies between the beamgenerator 9 and detector 10, such as when the perforations 4 are in-linewith the optical beam. The minimum detected signal occurs when the mostbeam-attenuating material lies between the beam generator 9 and detector10. Both extremes are shown in FIG. 2. By pre-calibration, thedifference between maximum and minimum signals can be used to controlthe printing head 6 to print indicia, in reverse, on a major surface ofthe transparent film 2.

[0072] The resulting printed medium 15′ has an adhesive applied to itslowermost surface, i.e. the surface which was printed on to, at adhesiveapplication station 16. A release liner may then be applied to thatsurface to protect the adhesive from contamination atrelease-liner-application station 19 a.

[0073] The further release liner-carrying printed medium 15′ is advancedto a lamination station 17. A length of substrate 20 moulded from ABS,with a retro-reflective surface 22 is similarly brought to thelamination station 17. The substrate 20 is typically from 2.5 to 3.8 mmthick, preferably 3.2 mm thick.

[0074] Immediately prior to registration of the printed medium 15′ withthe substrate 20, the further release liner, if previously applied, isremoved from the adhesive-bearing surface of the printed medium atrelease-liner-removal station 19 b. The printed medium 15′ and substrate20 are laminated together, using pressure, as indicated by arrows B inthe station 17, thereby sandwiching the indicia between theretro-reflective surface 22 and the transparent film 2. The adhesive ispressure-sensitive, which is to say it acts to adhere the two components15′, 20 through the application of pressure. A suitable acrylic adhesiveis S2001, supplied by MACtac Europe SA. The release liner may havetransverse perforations corresponding to those 4 of the medium 1′.

[0075] The leading edge of the first printed length is brought intointimate contact with a length of substrate 20, having aretro-reflective surface 22. Either before or after lamination of theprinted length to the substrate 20 has been fully effected, theperforations are broken to provide a separate identification plate 40.

[0076] In an alternative arrangement, the medium 1′, having a shapedtransparent film 2 with correspondingly shaped opaque release liner 3 asbefore, is not delineated by transverse perforations 4, the line 4 beingthe intended location of a cut line or perforated line about whichindividual lengths will be provided. The printer 5 is actuated followingoptical monitoring of the passage of the medium 1′ passed an opticalsensing device 8, as above. An adhesive is applied to the printedsurface of the transparent film 2 which then has a further release linerapplied thereto to protect the adhesive from contamination.

[0077] The so-formed medium 15′ may be cut into substrate-sized lengthsat intended cut line 4 prior to removal of the further release liner atstation 19 b or subsequent to removal of that further release liner atstation 19 b, the latter being the most preferred.

[0078] The substrate 20 may be formed in many ways. The first is simplyto mould or extrude ABS or to cut a substrate to the desired shape andsize from a sheet of material and adhere, by lamination, aretro-reflective film to one major surface thereof. Suitableretro-reflective film materials are Diamond Grade and Engineer Graderetro-reflective sheeting supplied by Minnesota, Mining andManufacturing Company (3M) of St. Pauls, Minn., USA, although others maybe used. It is often beneficial to mould the surface of the substrate 20with a slightly textured or roughened surface to aid adhesion of theretro-reflective material thereto.

[0079] Other retro-reflective sheet materials which may be used areformed as a composite of a retro-reflective sheet material having anadhesive applied to both major surfaces thereof, the adhesive beingcovered by release sheets. The intended lowermost surface of theretro-reflective sheet material is adhered to a suitably sized length ofsubstrate by lamination following removal of the lowermost releasesheet. The substrate, with retro-reflective sheet material appliedthereto, can then be stored for subsequent use or can be usedimmediately by removing the uppermost release sheet, thereby exposingthe adhesive-covered retro-reflective surface. The printed upon surfaceof the transparent sheet is then laminated thereto. Such aretro-reflective composite obviates the need for an adhesive applicationstation 16 or to apply adhesive to the retro-reflective surface.

[0080] As one alternative, the ABS, or other plastics material fromwhich the substrate 20 is moulded, has a substrate-sized length ofretro-reflective material moulded therewith.

[0081] To effect such moulding, the leading edge of a length ofretro-reflective sheet material is placed, pulled or otherwise drawninto a mould, where it is clamped in place. One portion of the mouldthen closes on the sheet. Whilst one major surface of theretro-reflective material is in contact with the top of the mould, acavity is provided between the other major surface of theretro-reflective material and the bottom of the mould. A plasticsmaterial, such as ABS, is injected into the cavity. As the mould isclosed shut, the retro-reflective material is adhered to the substrate20. The length of retro-reflective material may be the same size as themould or it may be over-sized. If it is over-sized the excess will betrimmed off.

[0082] Such a method removes the need for forming a substrate length 20with a roughened surface and subsequently laminating a retro-reflectivesheet material thereto, thereby reducing the cost.

[0083] Referring to FIG. 5, a sectional view of a plate 40 madeaccording to the above-described method is shown. The substrate 20 is amoulded length of plastics material, such as ABS, which has a pluralityof reflective glass beads 21 retained therein which provide theretro-reflective surface 22. Adhered to the substrate 20 is atransparent plastics film 2, having indicia 43 printed thereon.

[0084] The substrate 20 shown in FIG. 5, is formed by moulding aplastics material in which is distributed reflective bodies, such asglass spheres of, say, up to 15 μm diameter. Once the plastics materialis forced into the mould, the glass spheres are allowed to settle bygravity (if their density is greater than that of the fluid plasticsmaterial) or rise to the surface (if their density is less than that ofthe fluid plastics material). As an alternative, selective drying bymicrowaves can be used to encourage the beads 21 to preferentially movetoward one surface. Other methods for achieving such a result are knownto the man skilled in the art.

[0085]FIG. 6 shows a plate 40′ having a substrate 20′, to which isattached a film 2 having indicia 43 printed thereon. In this substrate20′, the reflective particles 21 are substantially evenly distributedthroughout its' thickness. The number of particles 21 per unit volumemay be greater than as shown to achieve the necessary retro-reflectivityof the completed plate 50.

[0086] In this case, the particles 21 are not allowed to settle or riseto a surface. Alternatively, the concentration of particles 21 withinthe plastics material 20′ may be so great that they are unable topreferentially settle toward a particular surface or they may have adensity substantially equivalent to that of the fluid plastics material,thereby preventing any preferential settling of one component over theother.

[0087] Once the transparent plastics film 2 has been applied to thesurface of the substrate 20, 20′ it has a retro-reflective character.Whilst glass beads and other reflective particles do not have as high anabsolute reflective property as bespoke retro-reflective materials,because the film 2 is so thin, compared to a lens using a 3.2 mm thickacrylate sheet (as is considered in certain prior art applications), theretro-reflectivity of the plates 40, 40′ is sufficient to meet therequired standard.

[0088]FIG. 7 shows an identification plate 40 a, which can be fabricatedusing the above-described methods. The plate 40 a has a main bodyportion 44 with visible indicia 43.

[0089]FIG. 8 shows a plate 40 b with an extended portion 41 along theintended bottom edge thereof for tertiary indicia 42. Primary indicia 43are visible. Secondary indicia (not shown) may be printed on thetransparent film 2 to stand out against the main body 44′ of the plate40 b. The tertiary indicia 42 may comprise advertising or otherpersonalisations and may be printed “off-line” or may be printedconcurrently with, or consecutively to, the primary indicia 43. A whiteor other coloured backing layer may be applied to the substrate 20 overthe extended portion 41 to provide a backing for the tertiary indicia42. In a further embodiment, the tertiary indicia 42 may be printed in acolour which is visible against the substrate 20. The transparent film 2may be applied to the whole, part or none of the extended portion 41.The retro-reflective surface 22 may extend over some or all of theextended portion 41.

[0090] Clearly, with computer control of the printer 5, differentindicia can be printed on subsequent lengths of media 1, 1′. In the caseof vehicle licence plates, it is possible to print two identical sets ofindicia on subsequent lengths, one for the front and one for the rearplate, and then to print another two identical sets of indicia, and soon.

[0091] The printable media 1, 1′ may be pre-printed with generalinformation as secondary indicia. Such information may show themanufacturer, supplier or other personalisations, security informationand the like. Such pre-printing provides a greater degree of flexibilityfor a manufacturer with a small turnover of identification plates as anygeneral information is pre-printed and the printer 5 can be used tosimply print the desired specific, primary indicia 43, such as a licenceplate number. Thus, a manufacturer can hold supplies of the pre-printedprintable medium 1, 1′ and print primary indicia 43 as and whenidentification plates 40 are required.

[0092] Using process control printing, as is possible with the Astro-medQLS 4100 series printer, it is possible to simplify further, andcommensurately reduce the cost of, fabricating a licence plate.

[0093] One of the requirements of the British Standard referred to aboveis that the retro-reflective material of the vehicle's intended rearnumber plate is a certain shade of yellow. In Greece, for example, oneof the background colours of the plates must be blue. It is a furtherrequirement, within Europe, that a regional country identifier as wellas the Euro flag (EU Council Regulation 2411/98[3]) is provided on acar's licence plate when travelling from a ‘home’ country to a differentEuropean country. Because, conventionally, the country identifier issupplied printed on to the retro-reflective sheet material the costs areincreased. Furthermore, yellow and other coloured retro-reflectivematerials which meet the required standards are relatively expensive.

[0094] Using process control of the printer 5, it is possible to print atranslucent coloured marking material onto the transparent film 2.Further, it is possible to print a blue ‘Euro’ flag on to thetransparent film 2 and the country identifier as well as the primaryindicia 43 and any secondary and any tertiary indicia 42. The printer 5prints each of the primary 43, secondary and any tertiary indicia 42, aswell as the coloured translucent material on to the transparent film 2from dedicated printing ribbons 7. None of any of the respective markingmaterials need overlay any other, due to accurate and precise computercontrol of the print head 6.

[0095] Clearly if, as in the United Kingdom, the intended rear (yellow)and front (white) vehicle number plates are different colours, twomanufacturing lines will conventionally be used. An alternative is toalternate the coloured plates say, yellow and white, on a manufacturingline. This approach can lead to problems when one of a pair of platesis, say, spoiled or if, say, two white or two yellow coloured substratesare placed on the manufacturing line by mistake. Thus, by processcontrol printing, stock levels can be reduced as can the number ofmanufacturing lines needed.

[0096] The coloured translucent material applied to the film 2 allows awhite retro-reflective surface 22 to be used, the coloured translucentmarking material imbuing the so-formed plate with the required colour.Such white retro-reflective sheet materials are significantly cheaperthan those in the required shades of yellow and other colours. Thethickness of the coloured marking material applied to the film 2 is suchthat it only minimally interferes with the retro-reflective nature ofthe retro-reflective material. Such an approach may also be used toprovide the required colour of retro-reflective surface of the plates40, 40′ of FIGS. 3 and 4.

[0097]FIG. 9 shows a detail of the printer 5, having the thermalprinting head 6 and ribbon 7′. As the printable medium 1, 1′, having atransparent sheet 2 and release liner 3, passes over the ribbon 7′, theprinting head 6 is activated to transfer some of the pigmented waxand/or resin on the ribbon 7′ to the transparent sheet 3 through theapplication of heat and pressure.

[0098] Certain colours, such a black and red tend to be laid onto thetransparent film 2 such that the retro-reflective surface 22 is notvisible through those indicia. For those colours, a conventional singlelayer ribbon 7 wherein a single layer of wax and/or resin colouredmarking material is provided on a foil and is transferred to the film 2by the application of heat and pressure from the print head 6.

[0099] However, in some circumstances, and with some colours, it isnecessary to ensure that the so-printed indicia are of sufficientclarity and visibility when the transparent sheet 3 is adhered to theretro-reflective surface 22. In those circumstances a composite ribbon7′ is provided.

[0100] The composite ribbon 7′ comprises a dual layer of wax and orresin, the first 72, which is intended for contact with the transparentsheet material 2 is the desired colour and the second 71, which is tolie adjacent the retro-reflective surface 22 of the substrate 20 in thecompleted plate 40, 40′ is opaque, usually white. Using single layer aswell as composite ribbons 7′ ensures that the printed primary, anysecondary and/or any tertiary indicia 42, 43 are visible and alsoensures that the retro-reflective surface 22 underneath the indicia 42,43 does not show through during use.

[0101] A further advantage of moulding the substrate 20, 20′ is that itcan be formed with a cavity in its' rear surface. The cavity can besized and formed such that an electrical device can be housed therein.Such devices may be sensors, signal emitters or transponders. An examplemay be a transponder used for traffic monitoring across a road network,for example, across automatically charged toll roads. Alternatively, avehicle security device may be mounted therein, to warn of, say, theftof the number plates of a vehicle. A host of devices may be housed insuch a cavity. In prior art plates, where a clear substrate is appliedover the retro-reflective material, the indicia being sandwichedtherebetween, it is not possible to provide such a cavity as any deviceinstalled in such a cavity would obscure part of the retro-reflectivematerial.

[0102]FIG. 10 shows a specific embodiment of a licence plate 100 made inaccordance with the methods described above. The licence plate 100bearing indicia 43 is constructed to be tamper evident and has a firstportion 102 located between two second portions 103. No cleardelineation of the portions 102, 103 is visible from the front of theplate 100, as shown in FIG. 10.

[0103]FIG. 11 is a side elevation of the plate 100. The plate 100 isformed from an elongate ABS substrate 20 having opposed first and secondfaces 106, 107.

[0104] The first face 106 is retro-reflective, either having aretro-reflective sheet material adhered thereto or havingretro-reflective particles embedded therein. A translucent sheetmaterial 2 having indicia 43 printed thereon is adhered to theretro-reflective surface 106.

[0105] The substrate 20 has lines of weakness 110 formed in the secondface 107. These take the form of channels or grooves cut into or mouldedwith the substrate 20.

[0106] As shown in FIG. 12, lines 110 extend across the width of thesecond face 107.

[0107] Adhered to the face 107 are sticky pads 111, each being coveredby a release layer as is known in the art. A pad 111 is present on eachside of the lines 110. The pads do not extend the full width of the face107.

[0108] To fit the plate 100 to a vehicle, the release layer is removedfrom each sticky pad 111 and the plate pressed onto the vehicle. Thepads comprise a contact adhesive which adheres the plate 100 to thevehicle.

[0109] If the substrate 20 is moulded, the lines 100 are formed duringpart of the moulding process. As one alternative, the lines 100 could bemilled out from the substrate 20.

[0110] A thief or other unscrupulous person who attempts to remove theplate 100 from a vehicle will need to prise the plate 100 away from thevehicle. The easiest point of attack is at either end of the plate 100.The force required to remove the sticky pads 111 from the vehicle bumperis substantial, whereas the force required to snap the plate 100 about aline of weakness 110 is less. Accordingly, as an attempt is made toprise the plate 100 from the vehicle, the plate will fracture about aline of weakness 110. Once a fracture occurs, delamination of the film 2adjacent the fracture line occurs, ruining the appearance of the plate100 and ensuring that the plate 100 cannot be used again, as indicatedin FIG. 13.

[0111] Further, should a person attempt to remove the film 2 with theindicia 43 from the plate 100, the strength of the adhesion of the film2 to surface 106 of the plate 100 causes the film 2 to stretch as it isremoved, thereby ruining the appearance of the indicia 43 and film 2.

[0112] As a further embellishment, an electric contact can be madeacross the line of weakness 110, so that upon an attempt to remove theplate 100 from a vehicle the contact is broken and an alarm sounds. Thecontact may be directly wired to the vehicles on-board alarm system.

[0113] The plate 100 appears from the front as a ‘normal’ licence plate,thus the unsuspecting vehicle licence plate thief will not know untilsuch times as the plate 100 breaks in his hands that he cannot remove itintact.

[0114] Vehicles which would benefit from having secure, un-stealable, ortamper evident, licence plates are those for the military, police,diplomatic service, security vans and the like. However, clearly anyvehicle could benefit from such tamper evident plates 100.

[0115] In the above-described methods a thermal transfer printer isused, FIG. 14 shows an ink jet printer 5′ having an ink jet head 67 witha UV curing lamp 66 to dry to so-applied ink, which could be used inplace of the thermal transfer printer. A further release layerapplication station may be present subsequent to application of theadhesive at station 16.

[0116] Other variations and modifications to the apparatus may be madewithout departing from the scope of the invention. For example, thesignal processing means 11 may be used to control each stage of themethod, conveying, printing, lamination, separation of perforations andso on. The optical beam generator and detector system may be a duplexsystem wherein the output of the beam is constantly monitored by afurther detector, the signal utilised by the processing means 11 being aratio of the two detected signals, thereby normalising for beam strengthfluctuation. The optical beam generator may be a simple light sourcesuch as a small bulb held in a tube, a diode or any other radiationsource which would be suitably attenuated by the release liner 3. Theadhesive which is used to ensure lamination of the printed medium 15 andthe substrate 20 may be applied to the retro-reflective surface 22 ofthe substrate 20.

[0117] The methods disclosed herein can be used to manufacture vehiclelicence plates as well as other signage—warning signs, direction signs,room-use indicators and so on. Frangible portions may be used to ensurethat any such signs may not be removed from their intended locationwithout them fracturing or otherwise becoming obviously removed.

1-32. (cancelled)
 33. A method of manufacture of an identificationplate, the method comprising: advancing a relatively thin transparentsheet material having an opaque release liner in contact with a firstmajor surface thereof to a printing station; printing indicia in reverseon to a second major surface of the sheet material; securing the printedsheet material to a relatively thick substrate having a retro-reflectivesurface such that the printed surface is in contact with, or at leastadjacent to, the retro-reflective surface.
 34. A method according toclaim 33 further comprising the steps of: optically sensing passage ofthe leading edge of the relatively thin transparent sheet material as itadvances toward the printing station by attenuation of an optical beamby the opaque release liner; and removing the opaque release liner fromthe relatively thin transparent sheet material subsequent to securingthe relatively thin transparent sheet to the relatively thick substrate.35. A method of manufacture of a vehicle identification plate, themethod comprising: conveying a relatively thin transparent sheetmaterial toward printing means; optically sensing the passage of therelatively thin transparent sheet as it is conveyed toward said printingmeans; actuating printing means in response to said passage of therelatively thin transparent sheet material to print indicia in reverseon a second major surface of the relatively thin transparent sheetmaterial; and securing the printed relatively thin transparent sheetmaterial to a relatively thick substrate having an entireretro-reflective surface such that the printed second major surface isin contact with, or at least adjacent to, the entire retro-reflectivesurface.
 36. A method according to claim 33, comprising the preliminarystep of securing a retro-reflective sheet material to a major surface ofthe relatively thick substrate and thereby forming the entireretro-reflective surface.
 37. A method according to claim 35, comprisingthe preliminary step of securing a retro-reflective sheet material to amajor surface of the relatively thick substrate and thereby forming theentire retro-reflective surface.
 38. A method according to claim 33,comprising the preliminary step of locating a retro-reflective sheetmaterial within a mould and injecting plastics material into the mould,thereby forming a relatively thick substrate with an entireretro-reflective surface.
 39. A method according to claim 35, comprisingthe preliminary step of locating a retro-reflective sheet materialwithin a mould and injecting plastics material into the mould, therebyforming a relatively thick substrate with an entire retro-reflectivesurface.
 40. A method according to claim 33, comprising the preliminarystep of locating reflective particles in a molten plastics material toform a plastics matrix and moulding that matrix to form a substratehaving an entire retro-reflective surface.
 41. A method according toclaim 33, comprising printing, at the printing station, over the entiremajor surface of the transparent sheet material.
 42. A method accordingto claim 33, comprising pre-printing some markings on the to-be printedupon major surface of the relatively thin transparent sheet material.43. A method according to claim 33, comprising printing, at the printingstation, in different colours and shades over distinct portions of theto-be printed upon major surface of the relatively thin transparentsheet material.
 44. A method according to claim 33, comprising supplyingthe relatively thin transparent sheet material from a roll of relativelythin transparent sheet material.
 45. A method according to claim 44,wherein the roll of relatively thin transparent sheet material is shapedto have a repeating pattern, each repeat being a substrate-sized length.46. A method according to claim 33, comprising supplying the relativelythin transparent sheet material as individual substrate-sized lengths.47. A vehicle identification plate comprising a relatively thicksupporting substrate having an entire retro-reflective major surface anda relatively thin transparent sheet material having indicia printedthereon, the transparent sheet material being adhered to theretro-reflective major surface such that the indicia are located incontact with, or at least adjacent to, the retro-reflective majorsurface.
 48. An identification plate comprising a relatively thicksupporting substrate having a retro-reflective major surface and arelatively thin transparent sheet material an entire major surface ofwhich having marking material applied thereto, the relatively thintransparent sheet material being adhered to the retro-reflective majorsurface such that the marking material is in contact with, or at leastadjacent to, the retro-reflective major surface.
 49. A plate accordingto claim 47, wherein the retro-reflective major surface of therelatively thick substrate comprises a retro-reflective sheet material.50. A plate according to claim 48, wherein the retro-reflective majorsurface of the relatively thick substrate comprises a retro-reflectivesheet material.
 51. A plate according to claim 47, wherein therelatively thick substrate comprises a plurality of reflective particlesretained within a plastics matrix, the retro-reflective major surfacebeing retro-reflective by virtue of at least some of the particles beinglocated at and/or protruding from that surface.
 52. An identificationplate comprising a laminate of a relatively thick substrate and arelatively thin transparent sheet material having indicia printed on amajor surface thereof, the relatively thick substrate comprising aplastics matrix material in which is retained a plurality of reflectiveparticles, wherein the indicia are in contact with, or are at leastadjacent to, a major surface of the substrate and the transparent sheetmaterial provides a lens for the reflective particles at that majorsurface, thereby providing the plate with a retro-reflective character.53. A plate according to claim 48, wherein the reflective particles areuniformly distributed throughout the substrate.
 54. A plate according toclaim 52, wherein the reflective particles are uniformly distributedthroughout the substrate.
 55. A plate according to claim 48, wherein thereflective particles are preferentially distributed at or towards thefirst major surface of the substrate, thereby imparting aretro-reflective characteristic.
 56. A plate according to claim 48,wherein the reflective particles are formed from one of glass, forexample glass beads or spheres, or from a mineral or a plasticsmaterial.
 57. A plate according to claim 48, wherein the substratecomprises one of acrylonitrile butadiene styrene (ABS), polyethylene,Nylon (RTM) or other hard-wearing, impact and/or bend resistanceplastics materials.
 58. A plate according to claim 52, wherein thesubstrate comprises one of acrylonitrile butadiene styrene (ABS),polyethylene, Nylon (RTM) or other hard-wearing, impact and/or bendresistance plastics materials.
 59. A plate according to claim 48,wherein the support comprises a metal or an alloy thereof, such asaluminium or steel.
 60. A plate according to claim 48, wherein thetransparent sheet material is a polymer, preferably selected from one ofpolyvinyl chloride, polyester, polypropylene or polyethylene.
 61. Aplate according to claim 52, wherein the transparent sheet material is apolymer, preferably selected from one of polyvinyl chloride, polyester,polypropylene or polyethylene.
 62. A plate according to claim 48,wherein the transparent sheet material is less than 150 μm, preferablyless than 100 μm thick.
 63. A plate according to claim 48 wherein theplate has a main body for primary indicia and an extended portion forfurther indicia.
 64. A plate according to claim 63, wherein the extendedportion extends from one of the longer sides of the plate.
 65. A plateaccording to claim 48, wherein the transparent sheet material hasmarking material applied over some or all of the printed surfacethereof.
 66. A plate according to claim 48, having one or more lines ofweakness formed in the substrate.
 67. A plate according to claim 48,having a cavity in an intended rear face thereof for location of anelectrical or electronic device.
 68. A plate according to claim 52,wherein the transparent sheet material is less than 150 μm, preferablyless than 100 μm thick.
 69. A plate according to claim 52 wherein theplate has a main body for primary indicia and an extended portion forfurther indicia.
 70. A plate according to claim 69, wherein the extendedportion extends from one of the longer sides of the plate.
 71. A plateaccording to claim 52, wherein the transparent sheet material hasmarking material applied over some or all of the printed surfacethereof.
 72. A plate according to claim 52, having one or more lines ofweakness formed in the substrate.
 73. A plate according to claim 52,having a cavity in an intended rear face thereof for location of anelectrical or electronic device.
 74. A medium to bear indicia for use inan identification plate, the medium comprising a transparent plasticsfilm carrying a silicone material on a first major face thereof and anopaque liner carrying a pressure sensitive adhesive on a major facethereof; a second major face of the transparent plastics film beingprintable to, wherein the silicone layer and adhesive layer are incontact and the opaque liner and transparent film are seperable andre-attachable by virtue of the releasable interaction between siliconelayer and adhesive layer.
 75. A medium according to claim 74, whereinthe transparent plastics film is formed of a plastics material selectedfrom one of polyester, polyvinyl chloride, polypropylene orpolyethylene.
 76. A medium according to claim 74, wherein the opaqueliner is polypropylene.